feat: add KSampler live previews to assets sidebar jobs (#8723)

## Summary
Show live KSampler previews on active job cards/list items in the Assets
sidebar, while preserving existing fallback behavior.

## Changes
- **What**:
- Added a prompt-scoped job preview store (`jobPreviewStore`) gated by
`Comfy.Execution.PreviewMethod`.
- Wired `b_preview_with_metadata` handling to map previews by
`promptId`.
- Extended queue job view model with `livePreviewUrl` and consumed it in
both sidebar list and grid active job UIs.
  - Cleared prompt previews on execution reset.
- Added ref-counted shared blob URL lifecycle utility (`objectUrlUtil`)
and updated preview stores to retain/release shared URLs so each preview
event creates one object URL.
- Added/updated unit coverage in `useJobList.test.ts` for preview
enable/disable mapping.

## Review Focus
- Object URL lifecycle correctness across node previews and job previews
(retain/release behavior).
- Preview gating behavior when `Comfy.Execution.PreviewMethod` is
`none`.
- Active job UI fallback behavior (`livePreviewUrl` -> `iconImageUrl`).

## Screenshots (if applicable)
<img width="808" height="614" alt="image"
src="https://github.com/user-attachments/assets/37c66eb2-8c28-4eb4-bb86-5679cb77d740"
/>
<img width="775" height="345" alt="image"
src="https://github.com/user-attachments/assets/aa420642-b0d4-4ae6-b94a-e7934b5df9d6"
/>


┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8723-feat-add-KSampler-live-previews-to-assets-sidebar-jobs-3006d73d365081aeb81dd8279bf99f94)
by [Unito](https://www.unito.io)

src/composables/queue/useJobList.ts

@@ -7,6 +7,7 @@ import { st } from '@/i18n'
 import { isCloud } from '@/platform/distribution/types'
 import { useWorkflowStore } from '@/platform/workflow/management/stores/workflowStore'
 import { useExecutionStore } from '@/stores/executionStore'
+import { useJobPreviewStore } from '@/stores/jobPreviewStore'
 import { useQueueStore } from '@/stores/queueStore'
 import type { TaskItemImpl } from '@/stores/queueStore'
 import type { JobState } from '@/types/queue'
@@ -96,6 +97,7 @@ export function useJobList() {
   const { t, locale } = useI18n()
   const queueStore = useQueueStore()
   const executionStore = useExecutionStore()
+  const jobPreviewStore = useJobPreviewStore()
   const workflowStore = useWorkflowStore()
 
   const seenPendingIds = ref<Set<string>>(new Set())
@@ -256,6 +258,11 @@ export function useJobList() {
         String(task.promptId ?? '') ===
         String(executionStore.activePromptId ?? '')
       const showAddedHint = shouldShowAddedHint(task, state)
+      const promptKey = taskIdToKey(task.promptId)
+      const promptPreviewUrl =
+        state === 'running' && jobPreviewStore.isPreviewEnabled && promptKey
+          ? jobPreviewStore.previewsByPromptId[promptKey]
+          : undefined
 
       const display = buildJobDisplay(task, state, {
         t,
@@ -275,7 +282,7 @@ export function useJobList() {
         meta: display.secondary,
         state,
         iconName: display.iconName,
-        iconImageUrl: display.iconImageUrl,
+        iconImageUrl: promptPreviewUrl ?? display.iconImageUrl,
         showClear: display.showClear,
         taskRef: task,
         progressTotalPercent: